Vinification

Vinification

Oak Ageing

This is a complex topic which is not always readily understood and is sometimes treated as a simple ‘cosmetic’ enhancement of the wine. Oak ageing is in fact a very old practice and is designed in current times to give greater depth of flavour, interest and complexity to certain wines. The base wines need to be of sufficient structure and quality to start with, to be suitable for oak ageing.

This is a complex topic which is not always readily understood and is sometimes treated as a simple ‘cosmetic’ enhancement of the wine.

Oak ageing is in fact a very old practice and is designed in current times to give greater depth of flavour, interest and complexity to certain wines. The base wines need to be of sufficient structure and quality to start with, to be suitable for oak ageing.

Oxygenation

An important, but less talked-about, effect of ageing wine in barrels is that this allows a very slight and controlled exposure to oxygen. Normally, winemakers do all they can to avoid exposing their wines to air, but in this case the low-level oxidation that barrels permit is beneficial to the structure and character of the wine.

Source and Type of Oak

Many factors are involved in the use of oak for ageing wines. The type of oak can make a difference – whether it is American or French oak, and if French is it from the forests of Limousin, Troncais or Allier? The oak used for making wine barrels is thus influenced by a number of factors. Where is the barrel from? What regional variations have occurred with oak sourced from different forests? How was it dried? How was it toasted? What standard practices are employed by the cooperage that made the barrel? Toasting refers to the firing inside the barrel during its making (cooperage) and wine-makers may specify the level of ‘toast’ they require, as this will have an effect on the wine.

A key difference in the effect of oak barrels is whether they are made of French or American oak. If you ever get a chance to try side-by-side cask samples of the same wine aged in French and American oak, take it: the differences are marked. The relatively wide-grained American oak imparts a much stronger flavour, with more obvious sweet vanilla flavours and spicy notes. French oak has a more subtle, slightly more savoury effect. Producers have to decide which suits their wine better, although cost can be a factor here: French barrels are much more expensive than American ones.

New or old barrels?

Age of the barrel is another important factor, with new barrels and previously used barrels each giving a different effect on the resultant wine.Many producers juggle their barrels carefully, ageing their wine in a mix of new and used barrels to avoid over-oaking it. Great care must be taken with the use of older barrels, since they can harbour bacteria and yeasts that might contaminate the wine.

Oak Barrel Influence - the effects


Subtle flavors are imparted to wine as it ages in the barrel. Different types of oak (French and American being the two most widely used) from different regions (Limousin, Nevers, Troncais, etc.) give differing levels of flavour to the wine (most often described as vanilla).
Wine, as it rests in the barrel, goes through subtle chemical changes, resulting in greater complexity and a softening of the harsh tannins and flavours present at the end of fermentation. The effect of specific wood on different wines is the subject of great discussion and experimentation among wine makers throughout the world.


A barrel essentially does two things: it allows a very slow introduction of oxygen into the wine; and it imparts the character of the wood into the wine. This diminishes as a barrel gets older. 50% of the extract from a barrel is achieved on the first use, 25% the second and less on subsequent uses.

 

The benefits

There are two ways in which a wine benefits from its contact with oak:

Firstly, for red wines, controlled oxidation takes place during barrel aging. This very gradual oxidation results in decreased astringency and increased colour and stability. It also evolves the fruit aromas to become more complex. Through a system of topping the wine (filling up the barrel due to evaporation) while it is in the barrel and racking the wine from barrel to barrel to clarify it, sufficient oxygen is introduced to the wine to have these beneficial effects over a period of several months. The barrels themselves allow a certain low-level of oxygenation.

 

Chemistry and Flavour


Secondly, oak wood is composed of several classes of complex chemical compounds, each of which contributes its own flavour or textural note to both red and white wines. The most familiar of these are vanilla flavours, sweet and toasty aromas, notes of tea and tobacco and an overall structural complexity of tannin that combines with the tannin from the fruit itself ,in the case of red wines. The specific compounds creating these delightful nuances in the finished wine are: volatile phenols containing vanillin; carbohydrate degradation products containing furfural, a component yielding a sweet and toasty aroma; “oak” lactones imparting a woody aroma; terpenes to provide “tea” and “tobacco” notes, and hydrolysable tannins which are important to the relative astringency or “mouth feel” of the wine
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The chemistry of the oak barrel can impart differing amounts and qualities of flavour and texture depending upon the barrel manufacturing techniques and type of oak used. American oak (Quercus alba) versus French oak (Quercus robur), sawn versus hand-split, air-drying versus kiln drying of the staves, and the use of boiling water, steam, natural gas, or wood fire to bend the staves are among the most important variables in the manufacturing process.  Barrel makers and wine makers all over the world hold widely differing opinions on the best way to make a barrel. One thing we can all agree on is that barrel making is an extremely complicated craft - there are no amateur barrel makers!

 

The choices and the results

 

Many of the best wines are fermented and/or aged in oak barrels. The barrels can be large or small, old or new, or a combination of these factors. The smaller the barrel, the newer the barrel, and the more time spent in the barrel, the more oak flavors will be imparted into the wine. The source of the wood is also very important as stated earlier. Barrels are made by cutting wood into long, narrow pieces called staves. After seasoning, the staves must be heated so they can be bent to form the barrel. Steaming is the cheap method. The best method is to expose them to a flame. The longer the flame exposure, the more toasted or charred the wood becomes. This greatly affects the flavours imparted to the wine.

 

Flavours ,Aromas and Quality

Oak provides flavour and aromatic support to the wine, whilst adding richer, fuller structure and complexity. On the nose, oak’s primary influence tends to accentuate aromas that centre around the spice rack, with clove, cinnamon, nutmeg, vanilla and “allspice” being common aromas derived from a wine’s time spent in oak. On the palate, oak’s influence turns towards the rich flavors of caramel, coconut, vanilla, cinnamon, clove, smoke, tea, mocha, toffee and butter.

 

The various choices regarding the use of oak all inevitably effect overall quality and clearly certain choices are more costly than others. There is thus a resultant effect not only on quality but on price as well.

 


Sulphur Dioxide (SO2)

Sulphur Dioxide is found in all wines to a greater or lesser extent. It has been the subject of great controversy and continues to be widely debated. It is the most widely used and the most controversial additive in winemaking. It has two main functions - to inhibit or kill unwanted yeasts and bacteria and to protect wine from oxidation.

Sulphur Dioxide is found in all wines to a greater or lesser extent. It has been the subject of great controversy and continues to be widely debated. It is the most widely used and the most controversial additive in winemaking. It has two main functions - to inhibit or kill unwanted yeasts and bacteria and to protect wine from oxidation.

 

Sulphur Dioxide has been linked to certain allergic reactions and is sometimes thought to be responsible for headaches and other adverse reactions to wine drinking. There is still debate over both these effects, although there does seem to be more and more evidence that these reactions are caused by the additive.

 

However, SO2 is essential in modern wine-making, and if used skillfully by a good wine-maker, should cause no adverse effects unless there is a defined allergy – which is rare.  

 

 

Used as an anti-oxidant and anti-septic, extra sulphur can be added to freshly picked grapes in the form of metabisulphite (which is also found in other consumables such as fruit juices and dried fruit) at the beginning of the production cycle, but sulphur levels are also adjusted during production. The reason for this is twofold. Free sulphur reacts with oxygen to prevent the oxidation of wine, keeping it fresh and preventing browning, while bound sulphur in wine inhibits the growth of unwanted microorganisms, acting as a disinfectant

White wines usually have higher doses of sulphur dioxide; red wines and bubbly are known to have lower amounts whilst sweet white wines may contain very high doses of sulphur dioxide.

Consumers should make a clear distinction between headaches and hangovers. If you are sensitive to sulphur, a headache is most likely to be triggered within hours of consumption, whilst a hangover is only felt the following day. Alcohol, causing dehydration, rather than sulphites, are the cause of hangovers

The Role of Sulphur Dioxide in Wine-making

A small amount of SO2 is produced naturally as a by product of fermentation, but most of the SO2 has been added by the winemaker. During white wine production, it is added at almost every stage of the process, and is more or less required after malolactic fermentation is complete. It is used to a lesser extent during red wine production, but is still a necessary component in many production techniques.

The Advantages

Sulfur Dioxide is a simple molecule, two Oxygen atoms bonded with one Sulphur atom. Its Chemical properties are actually quite similar to that of Carbon Dioxide, one of the most abundant molecules on Earth. But in terms of winemaking, using it effectively is critical in producing a wine that will stand the test of time.

The most important mechanism of action for Sulphur Dioxide is as an anti-microbial agent. It regulates the growth of harmful yeast and bacterial growth in the wine. However, the “good” yeasts used in the winemaking process have developed a resistance to SO2 over the years, allowing them both to live in harmony with each other. This gives the “good” yeasts as competitive advantage over the harmful yeasts in the fermentation process.

Another important role of Sulphur Dioxide lies in its anti-oxidant properties. This guards against browning and protects the fruit-like qualities of the wine. SO2 can bind with a molecule called acetaldehyde. It is also produced when a wine undergoes oxidation. When SO2 reacts with acetaldehyde, they bond together, producing a harmless, odorless molecule.

The Dis-advantages

If a winemaker uses too much SO2, it can kill the “good” yeast, halting fermentation before the desired end point. It can also stop malolactic fermentation from completing, yield wines that taste unfinished.

You can tell a wine that has too much Sulphur Dioxide by its characteristically pungent odor. It smells similar to that of a recently struck match. Although many people have trouble putting their fingers on this smell, it is largely sensed as an irritation of the nasal passage membranes.

Using Sulphur Dioxide for red wines presents a unique set of problems for winemakers. SO2 binds to a group of molecules called anthocyanins; which give red wines their color. When SO2 reacts with anthocyanins it renders them inert, and they lose their colour and properties. Luckily for winemakers, a large percentage of anthocyanins are bound to tannin molecules, safe-guarding them from the effects of SO2.

 

The description on wine labels ‘contains sulphites’ refers to the fact that SO2 has been added to the wine. It is, however, of little or no practical use since the level of SO2 contained in the wine is not mentioned. As stated previously, SO2 is an absolute necessity to produce quality wine which will keep, but the levels need to be kept to the minimum necessary.

 

The more a wine is tampered with or transported – particularly prevalent in the making of lower quality and bulk wines – the more SO2 is added in larger quantities to prevent oxidation and deterioration. This could be a contributory factor in cheaper wines having a more detrimental effect on the consumer.


The Charmat Method

The Charmat method (also called the "Italian Method") of producing sparkling wines, is often used in the crafting of Prosecco. This method forces the second fermentation to happen in a large pressurised stainless steel tank prior to bottling, rather than in the bottle like the traditional méthode champenoise. The Charmat method is a cheaper means of conducting the second fermentation and is best used on sparkling wines that are meant to be consumed young and relatively fresh.

 

The Charmat method (also called the "Italian Method") of producing sparkling wines, is often used in the crafting of Prosecco. This method forces the second fermentation to happen in a large pressurised stainless steel tank prior to bottling, rather than in the bottle like the traditional méthode champenoise. The Charmat method is a cheaper means of conducting the second fermentation and is best used on sparkling wines that are meant to be consumed young and relatively fresh.

 

This method is also called the bulk method, tank method or ‘cuve close’ (closed tank in French). Charmat method comes from the Frenchman Eugene Charmat who perfected the process. Sparkling wines made in the charmat method are usually made in larger quantities and are ready for sale soon after harvest. The whole process can be conducted in only a few weeks.

 

Tank-fermented sparklers tend to have a greater fruit character than traditional-method sparkling wines.

 

This difference occurs because in tank fermentation, the route from grape to finished wine is shorter and more direct than in bottle fermentation. Some winemakers use the charmat method because their goal is a fresh and fruity character sparkling wine. You should drink charmat-method sparklers young, when their fruitiness is at its maximum.

 

Prosecco is often produced using the Charmat Method. To achieve the proper balance of flavour, aroma, elegance, consistency and fine bubbles, the wine is kept in the tanks from 20 days (frizzanti) to 3 months, and can go up to 6 months for Cuveè and Prestige.

Charmat Method History

Maumèné was the first person who thought to speed up the fermentation process by fermenting sparkling wines in large vessels rather than bottles. In the mid 1800s he built an “Afroforo” machine, consisting of a fermentation tank which siphoned the wine off and bottled it. The method was difficult to reproduce on an industrial scale. The Italian, Martinotti  then took Maumèné’s idea, industrialised and employed wooden tanks, but the system was still not effective enough.

Finally, Frenchman Eugène Charmat found a way to turn Martinotti’s idea into a successful industrial system by using stainless steel tanks (autoclave), coated on the inside with a vitrified glaze resistant to attack by wine and acids.